Adult Trichinella spiralis were maintained in vitro using defined media and the material excreted/secreted (ES) during this time examined for proteolytic enzyme (proteinase) activity using an azocasein assay and gelatin-substrate gels. Several discrete proteinases in the size range 14–100 kDa were observed with optimal activity at pH 7·5. The use of a class-differentiating panel of proteinase inhibitors indicated that serine proteinases were predominant although some inhibition was evident in the presence of cysteine and metalloproteinase inhibitors. Of a panel of potential natural protein substrates tested, ES proteinases only degraded fibrinogen and plasminogen and degradation was, in part, susceptible to the action of serine, cysteine and aspartyl proteinase inhibitors. In addition, antibody harvested from immune but not normal mice inhibited ES proteinase activity, an observation of relevance to the immunobiology of Trichinosis.

The presence of superoxide dismutase (SOD) activity in the bovine lungworm Dictyocaulus viviparus was examined using the xanthine–xanthine oxidase assay system and by non-denaturing PAGE followed by specific enzyme staining. High levels of activity were detected in excretory–secretory (ES) products of adult worms and in soluble extracts of both the L3 and adult stages of the parasite. Stage-specific and ES-specific activities were indicated by differences in SOD isoenzyme profiles between adult and larval parasite extracts and between adult extract and ES products, with a fast migrating activity being specific to ES products. All isoenzymes were sensitive to cyanide, indicating copper/zinc dependency. The antigenicity of ES SOD was demonstrated by a reduction in SOD activity in both the chemical assay and non-denaturing PAGE following incubation of parasite ES products with IgG antibody purified from serum of infected or vaccinated bovine hosts. The high level of SOD activity released by adult D. viviparus may be a reflection of the problems faced by a parasite occupying an oxygen-rich environment. Antibody inhibition of SOD may, therefore, be an important target of protective immunity.

Proteinase activities were examined in extracts and excretory–secretory (ES) products of the infective and adult stages of the cattle lungworm, Dictyocaulus viviparus. Multiple enzyme activities were identified from each source, as defined by pH optima, substrate specificities, inhibitor effects and substrate gel electrophoresis. Serine-, cysteine- and metalloproteinases were identified, secreted materials being more active against protein substrates per unit protein than were extracts, and the particular proteinases produced varied with the developmental stage of the parasite. The antigenicity of these parasite proteinases was demonstrated by the inhibition of enzymic activity with Protein G-purified serum IgG antibody from both infected and vaccinated hosts and in the retardation of enzyme migration on electrophoresis of enzyme–antibody complexes. For the adult products, this confirmed that the enzymes concerned were of parasite origin, and not host-derived. These results argue for investigation of D. viviparus proteinases as targets for the antibody response in the limitation of parasite-mediated tissue damage and as the active principle behind the anti-D. viviparus vaccine.